Many vehicles and machines, such as, for example, automobiles and on and off highway trucks, include an internal combustion engine that provides power for the vehicle. A typical internal combustion engine includes a number of intake and exhaust valves that control the flow of gases to and from the combustion chambers of the engine. The engine may also include a valve actuation system, such as, for example, a cam-driven valve actuation system, to control the actuation timing of the engine valves.
The overall performance of the internal combustion engine may be improved by using auxiliary valve actuators, such as, for example, hydraulically powered actuators, that actuate the engine valves to selectively implement variations on the cam-driven valve timing. For example, the auxiliary valve actuators may be used to actuate the exhaust valves of the engine to implement an “engine braking” cycle. In an engine braking cycle, the auxiliary valve actuators open the exhaust valves of the engine when a piston associated with a combustion chamber is at or near a top-dead-center position of a compression stroke. This opening of the exhaust valves allows the air compressed by the piston in the combustion chamber during the compression stroke to escape from the combustion chamber through an exhaust passageway. In this manner, the pistons of the engine are selectively used as air compressors to absorb power instead of generating power in response to the combustion of fuel.
Because the auxiliary valve actuators are used only when the engine is experiencing selected operating conditions, the auxiliary valve actuators should avoid interfering with the operation of the cam-driven valve actuation system when the engine is experiencing other operating conditions. The performance of the engine may be negatively impacted if, for example, the auxiliary valve actuators inadvertently opened the exhaust valves during the intake stroke of the pistons. This type of interference may occur if the auxiliary valve actuators do not adapt to changes in the size of engine components due to thermal expansion.
To prevent such interference, the auxiliary valve actuators are typically separated from the exhaust valve assembly by a certain distance, which is commonly referred to as a “lash.” The lash may prevent inadvertent or unintentional opening of the engine valves by the auxiliary valve actuators when changes in temperature of the engine cause a change in size of the engine components. However, the auxiliary valve actuators must take up the lash before engaging the engine valves to open the engine valves. This may result in the auxiliary valve actuators requiring additional fluid and/or additional time to open an associated engine valve. To obtain the best engine performance, the actuation timing of the engine valves should be controlled precisely. Accordingly, the system that controls the auxiliary valve actuators must account for the lash in each actuation of the associated engine valves.
The auxiliary valve actuators must also be controlled in a manner to prevent over-actuation or over-extension of the engine valves that could result in collision between the actuated engine valve and the engine piston. For example, if the selected operating condition under which the auxiliary valve actuator is employed to actuate the engine valve is one in which the engine piston is at or near top-dead-center of the piston stroke, over-actuation or over-extension of the valve may cause it to make contact with the piston, resulting in possible damage to the engine. To obtain the best engine performance, the distance that the engine valves are moved by the auxiliary valve actuators, sometimes referred to as valve lift, should be controlled precisely. Accordingly, it is advantageous if the system that controls the auxiliary valve actuators must also limit the amount of valve lift in each actuation of the associated engine valves.
The auxiliary valve actuator illustrated in U.S. Pat. No. 6,708,656 to Chang incorporates an improved anti-lash mechanism that addressed problems recognized in prior devices. However, Chang does not provide a needed mechanism for controlling or limiting valve lift. It is desirable to provide an auxiliary valve actuator that addresses both of the lash and travel-limit issues within a single device that is relatively simple and robust.
The engine valve actuator of the present disclosure solves one or more of the problems set forth above.